Field of the Invention
This application is directed to cardiac valve prostheses and to apparatuses and methods for deploying such devices in a minimally invasive manner.
Description of the Related Art
A major type of heart disease is valvular insufficiency, also called valvular regurgitation, which is characterized by the improper closing of a heart valve. A heart valve consists of a number of leaflets—either two or three—that swing open to allow blood to flow forward (anterograde) out of a heart chamber, and then swing closed to form a tight seal, preventing blood from leaking backwards (retrograde). Valvular insufficiency may result from a variety of problems with the components which make up the valve—for example, the leaflets themselves may degenerate, the tissue cords which tether the leaflets to muscles within the heart may break, or the ring of tissue within which the valve is seated (called the “annulus”) may expand after heart attacks or from congestive heart failure. Each of these problems leads to a common element in valvular regurgitation: when closed, the edges of the valve leaflets no longer fit snuggly next to each other and allow retrograde flow.
Mitral regurgitation (MR) (insufficiency of the valve which connects the left atrium with the left ventricle of the heart) and tricuspid regurgitation (TR) (insufficiency of the valve which connects the right atrium with the right ventricle of the heart) contribute significantly to cardiovascular morbidity and mortality. MR is a debilitating disease that can lead to serious complications and possible death. Its symptoms include shortness of breath, rapid respirations, palpitations, chest pain, and coughing. MR leads to heart failure and pulmonary edema and also predisposes patients to other conditions, such as stroke, arterial embolus, and arrhythmias, including atrial fibrillation and lethal ventricular arrhythmias. Detection and timely effective treatment of MR leads to higher survival rates, decreased complications, and increased comfort for patients.
Currently, the only commercially available method of definitively repairing atrioventricular valvular regurgitation is open-heart surgery. In this procedure, the patient is first anesthetized and then subject to a thoracotomy. Access to the patient's heart is achieved by making a large incision, retracting the skin, muscle, and bony structures. The surgeon must stop the beating of the heart and cut it open to directly visualize the valve. The surgeon then may repair the valve surgically, or remove the valve and implant a prosthetic valve. This requires placing the patient on cardiopulmonary bypass, which involves applying a heart-lung machine to the patient that circulates oxygenated blood throughout the body in place of the working heart and lungs. After the heart is bypassed and is stopped, its structure can be visualized.
Although open-heart surgery is a successful method of repairing or replacing faulty heart valves, it poses a significant risk to the wellbeing of the patient, including death, severe injury, and disability. There is a risk of ischemic or other damage to the heart and other vital organs resulting from the discontinuance of the heart's normal function. The heart-lung machine may also cause abnormalities of the patient's circulatory, respiratory, hematologic and neurologic systems. There is a risk of stroke and other consequences from emboli released into the blood during the surgery and during initiation of cardiopulmonary bypass. There is a risk of heart attack. Significant damage occurs to the tissues and bone retracted from the patient's chest while gaining access to the heart. Post-operative complications such as wound infection, pneumonia, and venous thrombosis occur because of the extent of incisions and the patient's debilitated state. Also, cardiopulmonary bypass carries with it a risk of renal insufficiency, particularly in patients with borderline kidney function. Such patients may require dialysis after surgery due to the stress on the kidneys during bypass. Consequently, a patient's recovery can be painful, discomforting, long in duration, and costly.
A minimally invasive, beating-heart procedure that would not expose the patient to these risks is therefore desirable. Moreover, a limited surgical approach or percutaneous approach would decrease or eliminate the tissue trauma that occurs from the extensive incisions of open-heart surgery, sparing patients pain, improving recovery time, and decreasing post-operative complications.
A very large population exists that would benefit from an alternative method of valve repair. Approximately 10% of coronary artery bypass surgeries include mitral valve repair or replacement, which amounts to 75,000 to 100,000 of such procedures per year world-wide. In addition, significant MR and/or TR complicate 30-60% of patients with congestive heart failure, contributing to their impaired cardiac function and causing significant morbidity. However, because of the significant risks involved in open-heart surgery, many of the patients are unable to undergo valve repair. Thus, a successful percutaneous or minimally-invasive method of valve repair on the beating heart would have extraordinary clinical benefit.
No commercial products have been marketed that successfully repair the mitral valve of the human heart with a minimally invasive, beating-heart procedure. Several factors are responsible for this. First, the heart and its associated valves are not directly visualized or accessible. One can use imaging techniques such as fluoroscopy or echocardiography, but these provide a two-dimensional image and a limited field of view. Three-dimensional imaging technologies, including advanced forms of echocardiography, are available but only in a limited number of medical centers and only to very few clinicians trained to use them. Second, it is extremely difficult to immobilize the rapidly moving heart valve leaflets for repair purposes while the heart is beating. Not only are the leaflets moving back and forth rapidly, but also they each have a different shape and geometry. Thus, no single device or methodology has successfully been used to repair heart valves in a minimally invasive manner on a beating heart.
Efforts have been made to commercialize catheter based valve clip devices, though such devices are not yet approved for use in the United States. These devices are delivered by a catheter system percutaneously on a catheter device that is articulated to steer a clip device into place. The catheter system is placed over a guidewire. The device has a dilator that facilitates insertion into the left atrium. Thereafter, the dilator is removed and the clip is advanced at the distal end of an inner portion of the catheter system through an outer portion of the catheter system into the left atrium. The inner portion is adjusted to orient the clip such that the clip points down toward the left ventricle. Once pointed downward, arms of the clip are opened. An innermost portion of the catheter system is then projected from the left atrium into the left ventricle, below the valve leaflets. Thereafter, the clip is retracted and closed to hold the leaflets together to reduce MR.
Although these clip devices can be explained relatively simply, the actual use is not simple. For example, steering and orienting the clip is a delicate operation that requires skill foreign to most cardiologists. The delivery device is relatively large at 24 French. It is heavy and rigid and more analogous to a robotic arm than to generally much more flexible devices regularly used by cardiologists. Because of its rigidity, it is steered using dials that actuate a complex mechanism to orient it in three degrees of freedom. This intricate control system for orienting the rigid arm is only accurately positioned through the use of complex imaging technologies. The rigidity of the system eliminates tactile feedback to the doctor and thus imaging is the only means for achieving and/or confirming placement.
While technically able to repair a mitral valve through peripheral access, these devices and the procedures in which they are used still are very costly to the patient and to the health care system in general. While these clips devices are described as being able to release, re-approach, and recapture the leaflets, such re-working procedures increase the overall procedure time which is disadvantageous for the patient and the physician. For example, the MitraClip procedure is indicated as taking 2 to 4 hours, which is comparable to open heart valve repair surgery. In practice, the procedure can take two to three times longer than this due to poor initial placement, release and re-grasping efforts. Also, the patient must be under general anesthesia, and both an interventional cardiologist and an echo cardiologist must be present during the procedure. These and other aspects of the MitraClip design discussed in the EU Heart Journal article of May 23, 2011 make it inconvenient and costly to use.